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CONNECTICUT 


Agricultural  Experiment  Station 


s 


NEW  HAVEN,  CONN. 


BULLETIN  225 


JANUARY,  1921 


ENTOMOLOGICAL  SERIES,  No.  28 


A  STUDY  OF  THE  BULB  MITE. 


By  Philip  Garman. 


Figure  1.     Section  of  infested  bulb,  and  a  mite  greatly  enlarged. 


CONTENTS 


Page 
114 
115 
115 
115 


Officers  and  Staff  of  Station.  . 

A  Study  of  the  Bulb  Mite.  .  . 

Distribution  of  the  Species .  .  . 

The  Name  of  the  Bulb  Mite . 

Description 117 

Host  Plants  Infested  and  In- 
jury resulting  from  the  Infes- 
tation   119 

Life  History 122 


Page 

The  Dimorphic  or  Heteromor- 

phic  Male 123 

The  Hypopus 124 

Migration  of  the  Species 126 

Tabular    Life    History    of   the 

Bulb  Mite 126 

Other    Species    of    Mites    and 

Predaceous  Enemies 127 

Control   Measures 130 

Conclusions 132 


The  Bulletins  of  this  Station  are  mailed  free  to  citizens  of  Connecticut 
who  apply  for  them,  and  to  others  as  far  as  the  editions  permit. 


CONNECTICUT  AGRICULTURAL  EXPERIMENT  STATION 

OFFICERS  AND  STAFF 


BOARD  OF  CONTROL. 
His  Excellency,  Marcus  H.  Holcomb,  ex-officio,  President. 

James  H.  Webb,  Vice  President Hamden 

George  A.  Hopson,  Secretary New  Haven 

E.  H.  Jenkins,  Director  and  Treasurer New  Haven 

Joseph  W.  Alsop Avon 

Charles  R.  Treat Orange 

Elijah  Rogers Southington 

William  H.  Hall South  Willington 


STAFF. 

Administration.  E.  H.  Jenkins,  Ph.D.,  Director  and  Treasurer. 

Miss  V.  E.  Cole,  Librarian  and  Stenographer. 

Miss  L.  M.  Beautlecht,  Bookkeeper  and  Stenographer. 

WiLi-iAM  Veitch,  In  charge  of  Buildings  and  Grounds. 
Chemistry. 

Analytical  Laboratory.  E.  Monroe  Bailey,  Ph.D.,  Chemist  in  Charge. 

R.  E.  Andrew,  M.A.,  C.  E.  Shepard,  I 

H.  D.  Edmond,  B.S.,  Owen  Nolan,       * 

Frank  Sheldon,  Laboratory  Assistant. 

V.  L.  Churchill,  Sampling  Agent. 

Miss  Alt  a  H.  Moss,  Clerk. 


Assistant  Chemists. 


Protein  Research. 
Botany. 


Entomology. 


Forestry. 


Plant  Breeding. 


Vegetable  Growing. 


T.  B.  Osborne,  Ph.D.,  D.Sc,  Chemist  in  Charge. 

G.  P.  Clinton,  Sc.D.,  Botanist. 

E.  M.  Stoddard,  B.S.,  Assistant  Botanist. 

Miss  Florence  A.  McCormick,  Ph.D.,  Scientific  Assistant. 

G.  E.  Graham,  General  Assistant. 

Mrs.  W.  W.  Kelsey,  Stenographer. 

W.  E.  Britton,  Ph.D.,  Entomologist;  State  Entomologist. 

B.  H.  Walden,  B.Agr.,   M.  P.  Zappe,  B.S., 
Philip  Garman,  Ph.D.,     Samuel  T.  Sealt, 
John  T.  Ashworth, 
Miss  Gladys  M.  Finlet,  Stenographer. 

Walter  O.  Fillet,  Forester,  also  State  Forester  and 

State  Forest  Fire  Warden, 
A.  E.  Moss,  M.F.,  Assistant  State  and  Station  Forester. 
H.  W.  HicocK,  M.F.,  Assistant. 
Miss  Pauline  A.  Merchant,  Stenographer. 

Donald  F.  Jones,  S.D.,  Plant  Breeder. 

C.  D.  Hubbell,  Assistant. 


Assistant 

Entomologists, 


Press  of  The  Wilson  H.  Lee  Company. 


A  Study  of  the  Bulb  Mite 

(Rhizoglyphus  hyacinthi  Banks.) 


By  Philip  Garman,  Ph.D. 


Inspection  of  over  a  million  bulbs  in  Connecticut  during  1919 
brought  to  light  the  significant  fact  that  nearly  all  shipments  con- 
tained the  bulb  mite  R.  hyacinthi  Banks.  In  many  shipments 
only  a  few  infested  bulbs  were  found,  but  in  others  as  high  as 
fifteen  to  twenty  per  cent,  were  apparently  destroyed.  Ship- 
ments were,  however,  frequently  delayed  in  transit  according  to 
reports,  a  state  of  affairs  doubtless  responsible  for  the  poor  condi- 
tion of  many  bulbs  when  they  arrived  at  their  destination.  Rotten 
bulbs,  too,  are  not  always  the  result  of  mite  infestation  alone, 
there  being  several  other  causes  of  rot  and  disease- — but  the  almost 
universal  presence  of  the  mites  in  decayed  bulbs  has  led  to  the 
present  study  of  the  life  history,  habits  and  control  of  the  pest. 

Woods^  claims  that  the  Bermuda  lily  disease,  caused  in  part  by 
mite  infestation,  results  in  a  yearly  loss  of  20  to  60  per  cent,  of 
the  entire  crop  where  the  plants  are  forced.  Destruction  of  bulbs 
has  also  been  noted  by  many  other  American  and  European 
workers. 

The  injurious  effects  of  the  species  in  Connecticut  were  first 
described  in  the  report  of  the  State  Entomologist  for  1915^,  when 
3000  Easter  lilies  were  destroyed.  Since  then,  no  specific  case 
in  which  extensive  damage  was  done,  has  been  reported  to  this 
office,  but  there  is  doubtless  a  small  per  cent,  of  loss  each  year 
which  should  be  prevented  by  proper  inspection,  care  and  treat- 
ment of  the  mite-infested  bulbs. 

Distribution  of  the  Species. 

The  bulb  mite  has  been  reported  in  foreign  shipments  to  various 
states  and  to  Canada.  Shipments  of  bulbs  to  Connecticut  come 
mostly  from  France,  Belgium  and  Holland,  but  what  is  apparently 
the  same  species  was  found  in  one  shipment  received  from  Japan. 
It  has  also  been  reported  in  shipments  of  bulbs  from  the  Bermuda 
Islands  and  thus  seems  to  have  a  fairly  wide  distribution. 

The  Name  of  the  Bulb  Mite. 

Banks^  in  1906,  listed  under  the  name  of  Rhizoglyphus  hyacinthi 
Boisduval  a  species  of  mite  which  he  found  in  bulbs.     Since  that 

lU.  S.  Dept.  Agr.  Div.  Veg.  Phy.  &  Path.  Bui.  14:  1897. 

2  Conn.  Agr.  Exp.  Sta.  Rep.  190:  1915. 

3  Banks,  N.,  Revision  of  the  Tyroglyphidae,  U.S.D.A.  Bur. Ent. Tech. 
Ser.l3:  21:  1906. 


116         CONNECTICUT   EXPERIMENT    STATION   BULLETIN   225. 

time  Americans  have  religiously  followed  the  name  hyacinthi  in 
preference  to  the  name  echinopus  of  European  authors.  Michael^ 
however,  places  hyacinthi  as  a  synonym  of  echinopus,  with  the 
remark  that  hyacinthi  of  Boisduval  is  a  nomum  nudum  being 
listed  without  description.  Michael  is  correct  in  this  statement, 
since  the  original  description  given  by  Boisduval  is  very  meager 
and  is  not  sufficient  for  purposes  of  identification.  However,  the 
description  of  echinopus  given  by  Fumouze  and  Robin^  shows 
that  the  latter  may  also  have  considered  a  different  species;  for 
the  species  in  hand  differs  from  it  (and  also  Michael's  description) 
in  important  particulars. 

The  most  striking  of  these  characters  are  the  chitinous  thick- 
enings on  the  fourth  pair  of  legs,  which  occur  both  in  normal  and 
heteromorphic  males.  Michael  states  that  the  only  species  bear- 
ing this  character  is  R.  crassipes  Haller,  which  was  originally 
described  as  an  American  species^,  but  crassipes  differs  (in  other 
particulars),  from  our  species,  and  we  are  forced  to  conclude  that 
either  the  chitinous  thickenings  have  been  overlooked  or  the 
species  may  be  different  from  all  described  species.  Inasmuch 
as  Michael  (1.  c,  p.  83)  says  emphatically  that  "there  are  not  any 
suckers  on  the  leg  of  the  male  of  any  species  except  R.  crassipes 
Haller"  we  are  able  to  conclude  that  he  must  have  examined  the 
species  which  he  described,  for  this  particular  character.  Exami- 
nation of  material  from  the  U.  S.  National  Museum  shows  chiti- 
nous thickenings  on  the  fourth  pair  of  legs  in  R.  hyacinthi  and  R. 
rhizophagus.  The  rather  frequent  presence  of  the  dimorphic  male 
excludes  the  species  in  hand  from  rhizophagus  and  refers  it  to 
hyacinthi.  As  already  intimated,  a  search  through  Boisduval's 
works  has  revealed  no  adequate  description  of  this  species  and 
either  his  name  hyacinthi  must  be  disregarded  or  the  authority 
changed  from  Boisduval  to  Banks.  The  latter  course  is  to  be 
preferred  and  the  name  Rhizoglyphus  hyacinthi  Banks  instead  of 
Rhizoglyphus  hyacinthi  Boisduval  should  be  used,  since  Boisduval's 
name  cannot  be  connected  with  any  known  species. 

For  convenience  the  description  given  by  Boisduval  is  quoted 
herewith.  Bank's  description  of  the  species  is  found  in  Bur.  Ent. 
Tech.  Ser.  Bui.  13,  p.  21,  1906  (pi.  V  fig.  49). 

Description  by  Boisduval. 
Entomologie  Horticole  p.  86:  1867. 

"Nous  ne  trouvons  mentionne  nuUe  part  I'acarus  de  la  Jacinthe,  nous 
ne  Savons  pa  s'il  n'a  pas  deja  ete  observe  par  quelque  naturaliste.  Nous 
lui  donnons  le  nom  provisoire  d'acarus  des  Jacinthes  Acarus  hya- 
cinthi.^' 


1  Michael,  A.  D.,  British  Tyroglyphidae  II:  p.  85:  1903. 

2  Jour.  Anat.  Phys  ,  V:  287:  1868. 

3  Haller,  Archiv  Naturgeschichte,  50:  218:  1884. 


A   STUDY    OF   THE    BULB    MITE.  117 

General  Description. 

Egg  (Fig.  2,  No.  6), — The  egg  is  ellipsoidal,  white  and  semitransparent; 
.12  by  .07  mm.  in  size. 

Larva  (Fig.  2,  No.  2), — Small,  white,  somewhat  ovoid  in  shape;  genital 
suckers  absent.  Cephalo-thorax  with  two  long  setae  on  the  frontal  margin 
above,  and  two  near  the  caudo-lateral  angle;  no  minute  bristles  between  the 
latter  as  in  the  adult;  venter  of  the  thorax  with  a  clavate  sense  organ 
(Fig.  2,  No.  3)  between  the  bases  of  the  first  and  second  coxae  on  each  side 
and  small  setae  mesad  of  these;  front  tarsi  with  strong  spines  as  in  the  adult, 
but  the  clavate  hair  much  longer  than  the  spine  immediately  beyond  it; 
tip  of  the  tarsus  with  three  slender  setae;  front  tibiae  with  the  usual 
long  setae  on  the  dorsum,  the  patella  (3rd  segment  from  end  beginning 
with  tarsus)  each  with  two  shorter  setae  on  the  dorsum  as  in  the  adult. 
Abdomen  with  one  pair  of  legs,  the  tarsi  of  each  of  which  bears  a  long 
heavy  spine  and  longer  seta  on  the  dorsal  surface  and  three  spines  on  the 
ventral;  tarsal  claw  very  stout;  tibiae  each  bearing  a  single  long  seta 
on  the  dorsal  surface;  lateral  margins  of  the  abdomen  with  four  setae  on 
each  side  and  a  pair  near  the  anal  opening. 

Size  shortly  after  emergence  from  the  egg,  .15-. 2  by  .1  mm.,  full  grown, 
.25  by  .15  mm. 

Protonymph  (Fig.  2,  No.l), — Similar  to  the  larva  in  size  and  shape  but 
larger  and  provided  with  four  pairs  of  legs  instead  of  three;  rostrum  as  in 
adult;  cephalo-thorax  as  in  adult;  with  two  long  setae  on  the  frontal  margin 
of  the  dorsum  and  two  near  the  caudo-lateral  angle;  no  minute  setae  be- 
tween the  latter;  the  front  tarsi  have,  in  common  with  the  adult,  a 
minute  clavate  hair  at  the  base  and  to  one  side  of  the  large  clavate  hair; 
and  between  the  larger  clavate  hair  and  the  spine  (immediately  beyond)  is 
a  smaller  spine  about  one-fifth  the  length  of  the  latter;  tip  of  front  tarsi 
with  three  slender  setae  each.  The  fouth  pair  of  legs  has  only  one  seta 
at  the  tip  of  the  tarsus  and  there  is  no  dorsal  spine  on  that  segment; 
however,  there  is  a  strong  lateral  spine  and  a  ventral  spine.  Judging 
from  the  spines  and  setae  on  the  tarsi  of  leg  three  in  the  larva  and  the 
protonymph,  the  fourth  pair  of  legs  of  the  protonymph  must  grow  in 
behind  the  third  pair  of  the  larva. 

This  stage  is  most  easily  distinguished  from  the  tritonymph,  which  it 
resembles  more  closely  than  other  stages,  by  the  appearance  of  the 
genital  suckers.  In  the  protonymph  only  two  make  their  appearance 
while  in  the  tritonymph  there  are  three  or  four  (see  Fig.  2,  No.  5).  There 
is  also  some  difference  in  the  tarsi  of  the  fourth  pair  of  legs,  the  latter  pos- 
sessing no  dorsal  spine  in  this  stage. 

Length  full  grown,  about  .4  mm.,  width  about  .2  mm. 

Deutonymph  or  hypopus  (Fig.  2,  No.  11), — Oval  in  shape,  dorsum  convex; 
venter  flat;  color  brown,  the  body  heavily  reinforced  throughout  with 
chitin.  Rostrum  apparently  reduced  to  a  small  cylindrical  projection 
entirely  covered  by  the  cephalo-thorax;  distal  end  of  rostrum  with  two 
long  setae,  and  a  smaller  one  at  the  base  of  each.  Mouth  parts  wanting; 
cephalo-thorax  with  two  long  setae  on  the  front  margin  placed  closely 
together,  and  about  the  same  length  as  the  long  setae  of  the  rostrum; 
legs  for  the  most  part  without  the  heavy  spines  of  the  adult,  the  latter 
replaced  in  most  cases  by  setae;  tarsal  claws  long,  curved  rather  sharply; 
tarsi  of  first  pair  of  legs  with  four  slender  setae  at  tip  and  two  near  middle 
of  ventral  surface.  There  is  also  a  heavy  spine  on  the  ventral  surface; 
a  large  clavate  hair  nearly  half  as  long  as  the  segment,  and  a  smaller 
clavate  hair  and  small  seta  on  caudal  surface  near  the  larger  one.  In 
front  of  the  larger  clavate  hair  there  is  also  a  long  seta;  front  tibia  with 
a  long  seta  on  dorsum  and  a  single  spine  on  each  side;  patella  with  a 
single  seta  at  tip  instead  of  two,  as  in  all  other  stages.  Abdomen  with 
conspicuous  expulsory  vesicles  on  either  side;  margin  composed  of  thick 
heavy  chitin,  which  shows  prominent  striations  under  magnification;  ven- 
ter with  conspicuous  suckers  as  in  Fig.  2,  No.  11,  one  on  each  side  of  the 


118  CONNECTICUT    EXPERIMENT   STATION   BULLETIN   225. 

anal  opening,  two  caiidad  of  this,  then  a  row  of  four,  and  finally  two  more 
Surrounding  the  eight  caudal  suckers  is  a  squarish  ring  which  is  thickened 
at  each  of  its  four  corners,  making  it  appear  as  if  four  additional  suckers 
were  present;  conspicuous  lines  of  chitin  on  the  venter,  extending  cepha- 
lo-mesad  from  the  anal  opening  and  each  coxa  of  legs  III  and  IV;  third 
and  fourth  pair  of  legs  short  and  usually  hidden  by  the  overhanging  body 
wall  when  viewed  from  above;  tarsi  with  four  setae  and  two  heavy  spines 
at  tip;  tibiae  with  a  long  seta  near  tip,  on  dorsum;  margin  of  abdomen 
with  four,  minute  marginal  setae. 

Length,  .2-.3  mm.     Width  .13-.  18  mm. 

Tritonymph  (Fig.  2,  No.  9),- — Color  white,  translucent  or  semiopaque,  legs 
brown  or  tinged  with  pink. 

Rostrum  and  cephalo-thorax  agreeing  in  nearly  all  particulars  with  the 
adult  female.  Abdomen  as  in  the  adult  as  regards  setae;  but  the  geni- 
talia imdeveloped;  the  genital  suckers  consist  of  four  indistinct  suckers 
closely  approximated  (Fig.  2,  No.  9). 

Length  .5-. 6  mm,  width  .3-. 3. 5  mm. 

Adult  (Fig.  3,  Nos.  12-15;  Fig.  2,  Nos.  4,  5,  7  and  8),— Color  white,  body 
somewhat  transparent;  legs  epimera  and  rostrum  brown,  sometimes  with 
a  pinkish  hue. 

Rostrum  with  large  mandibles,  which  are  chelate,  maxillary  palpi  with 
two  distinct  segments  closely  joined  to  the  rostrum  and  a  very  small 
projection  at  the  tip,  which  may  represent  a  third  segment.  Each  of 
the  longer  segments  with  a  minute  seta,  and  a  longer  seta  on  each  maxilla; 
cephalo-thorax  narrowed  rapidly  in  front,  the  sides  gently  curved,  the 
front  margin  with  two  long  setae  extending  beyond  the  rostrum  and 
placed  closely  together;  near  the  caudo-lateral  angles  of  the  dorsum  are 
also  two  long  setae  between  which  are  two  usually  minute  hairs;  venter 
of  cephalo-thorax  with  conspicuous  epimera,  the  front  epimera  being  united 
on  the  mesal  line;  between  the  first  and  second  epimera  on  each  side 
there  is  usually  a  small  seta;  first  two  pairs  of  legs  thicker  than  the  last 
two,  5-segmented,  the  tarsi  of  the  first  pair  provided  with  spines  and 
setae  as  follows:  a  large  clavate  sense  organ,  near  the  proxima  Imargin 
on  the  dorsum,  and  a  large  heavy  spine  just  distad  of  this;  a  much 
smaller  clavate  hair  at  one  side  of  the  larger  sense  organ,  about  half  its 
length;  between  the  larger  clavate  sense  organ  first  mentioned  and  the 
spine  distad  of  it  is  a  smaller  spine  about  one-third  its  length;  at  the  tip 
of  the  tarsus  above  there  is  also  a  large  spine  with  three  setae  surrounding 
it,  one  of  which  is  much  smaller  than  the  rest;  ventrad  of  the  tarsal  claw 
there  are  usually  three  or  four  heavy  spines,  grouped  together  and  another 
proximad  of  these;  there  is  a  long  seta  near  the  proximal  spine  and  a 
very  inconspicuous  one  on  the  opposite  surface  of  the  tarsus;  tarsal  claw 
not  sharply  curved;  tibia  with  a  long  seta  on  the  dorsum  near  the  distal 
end  which  is  often  as  long  or  longer  than  the  tarsal  segment;  there  is  a 
single  stout  spine  on  the  caudal  and  ventral  surface  of  this  segment;  the 
patella  has  two  closely  placed  setae  near  the  distal  margin  of  the  dorsum 
and  the  femur  has  a  single  long  seta  on  the  ventral  surface;  the  second 
tarsus  is  essentially  the  same  as  the  first,  except  that  the  smaller 
clavate  hair  or  sense  organ,  and  the  small  spine  (between  the  larger  hair 
and  the  spine  immediately  distad)  are  wanting;  one  seta  is  also  lacking 
from  the  tip;  the  third  and  fourth  pairs  of  legs  lack  the  clavate  sense 
organs  and  are  different  in  the  two  sexes.  In  the  female  and  normal  male 
the  third  pair  of  legs  are  similar;  there  is  a  long  thick  spine  at  the  tip  of 
the  tarsus,  above  and  below  which  is  a  long  slender  seta;  on  the  caudal 
surface  of  this  segment  there  is  also  one  seta  and  there  is  a  spine  on  the 
opposite  surface;  the  ventral  surface  has  a  spine  shortly  distad  of  the 
middle  and  a  group  of  about  four  ventrad  of  the  tarsal  claw;  the  latter  is 
sharply  hooked.  The  third  pair  of  legs  of  the  dimorphic  male  are  much 
thicker  than  the  third  pair  of  the  female  or  normal  male.  There  are 
four  long  setae  at  the  tip,  and  the  tarsal  claw  seems  to  be  fused  with  the 


A   STUDY    OF   THE   BULB   MITE.  119 

tarsal  segment  (Fig.  2,  No.  10);  the  fourth  pair  of  legs  differ  in  the  two 
sexes  but  are  the  same  in  dimorphic  and  normal  males.  In  the  female 
there  is  a  distal  spine  on  the  tarsal  segment  just  above  the  claw  and  one 
lateral  (caudal  surface)  and  one  ventral  spine  in  addition,  besides  a  group  of 
three  just  beneath  the  claw.  There  are  usually  three  setae,  one  above 
and  another  below  the  distal  spine  and  one  lateral  seta;  in  the  male  the 
distal  dorsal  spine  is  wanting,  being  replaced  by  a  chitinous  thickening 
sometimes  called  a  sucker;  proximad  of  this  is  still  another  thickening 
and  between  the  two  a  single  seta;  the  segment  possesses  the  usual  number 
of  spines  below  the  claw  on  lateral    and  ventral  surfaces  (Fig.  2,  No.  7). 

In  the  female  the  lateral  surfaces  of  the  abdomen  are  provided  with 
about  five  setae  on  each  side;  the  ventral  surface  with  three  minute  seta6 
on  each  side  of  the  genital  opening  and  one  between  the  third  and  fourth 
coxae,  a  small  one  in  front  of  and  to  one  side  of  the  third  coxae  and  a 
long  one  on  each  side  of  the  anal  opening;  the  genital  opening  forms  an 
inverted  V-shaped  figure  with  two  genital  suckers  on  each  side  (Fig.  3, 
No.  14);  the  dorsum  has  five  setae  on  each  side,  of  which  the  caudal  pair 
are  the  longest. 

In  the  male  there  are  the  usual  five  setae  on  lateral  and  caudo- 
lateral  surfaces  of  the  abdomen  and  one  minute  seta  between  the  third 
and  fourth  pairs  of  legs  on  ventral  surface,  and  a  smaller  one  in  front  of  and 
to  one  side  of  the  third  coxae;  genital  opening  as  in  Fig.  3,  No.  12  with  two 
genital  suckers  on  each  side.  Caudad  of  the  genital  opening  are  found 
two  larger  disc-like  suckers,  with  a  minute  seta,  caudad  and  cephalad, 
and  usually  a  row  of  four  longer  ones  caudad  of  the  suckers;  setae  of  the 
dorsum  as  in  female. 

Variations — There  seems  to  be  some  variation  both  in  the  length  of 
the  setae  of  the  legs  and  body  and  also  in  the  thickness  of  the  tarsal 
segments.  Of  seventeen  individuals,  however,  measured  with  microm- 
eter the  ratio  of  width  to  length  of  tarsus  IV  ranged  from  1-1.6  to  1-2. .5, 
both  sexes  being  examined.  There  is  also  a  great  variation  in  the  depth 
of  the  depressions  on  the  dorsum  of  the  adult,  they  being  almost  obliter- 
ated in  some  individuals. 

Length,  female  .47-. 95  mm;  male  .5-. 6  mm.  Width,  female  .3-4  mm; 
male  .25-. 3  mm. 


Host  Plants  Infested  and  the  Injury  Resulting  from 
THE  Infestation. 

Narcissus  (Plate  I,  b;  II,  a;  III,  b),  hyacinth,  tulip,  crocus  and 
Easter  lily  bulbs,  are  infested  by  the  bulb  mite.  In  the  laboratory 
it  has  been  reared  on  onions  and  potatoes,  and  is  probably  capable 
of  subsisting  on  almost  any  tuber  or  bulb.  Its  common  occurrence 
in  narcissus  and  lily  bulbs  may  be  due  to  the  fact  that  these  bulbs 
offer  least  resistance  to  attack  since  the  scales  are  loose  and  the 
mites  find  it  easy  to  penetrate  to  the  interior.  ,  Tuhps  are  least 
injured,  owing  to  their  outer  skin  and  tight-fitting  scales  which 
have  no  place  for  the  mites  to  enter.  Hyacinths  seem  to  be  less 
easy  to  penetrate  than  narcissus,  while  onions,  artificially  infested 
with  mites,  were  not  injm-ed  unless  they  were  partly  rotten  or 
bruised  in  the  beginning. 

That  the  mites  are  able  to  feed  on  healthy  tissue  seems  evident 
both  from  numerous  references  to  this  particular  ability  by  vari- 
ous writers  and  from  the  experience  of  those  connected  with  this 
office  in  the  case  of  the  Bermuda  hhes  already  mentioned.     A  small 


120         CONNECTICUT   EXPERIMENT   STATION   BULLETIN   225. 


Figure  2.  The  bulb  mite  (Rhizoglyphus  hyacinthi  Banks).  1.  Proto- 
nymph,  enlarged  about  80  times.  2.  Larva,  enlarged  about  80  times. 
3.  Larva,  sense  organ  of  the  ventral  surface  of  the  cephalothorax.  4. 
Front  tibia  and  tarsus  of  the  female.  5.  Fourth  tibia  and  tarsus  of 
male.  6.  Egg,  enlarged  about  80  times.  7.  Fourth  tibia  and  tarsus  of 
the  female.  8.  Front  tibia  and  tarsus  of  the  female.  9.  Tritonymph, 
enlarged  about  80  times.  10.  Fourth  tibia  and  tarsus  of  dimorphic  male. 
11.  Deutonymph  or  hypopus,  enlarged  about  80  times. 


A   STUDY   OF    THE    BULB    MITE. 


121 


Figure  3.  Adult  bulb  mite  {Rhizoglyphus  hyacinthi  Banks),  enlarged 
80  times.  12.  Male,  ventral  view.  13.  Female,  dorsal  view.  14.  Fe- 
male, ventral  view.     15.   Male,  dorsal  view. 

number  of  tests  have  been  conducted  by  the  writer  in  which 
mites  entered  and  fed  on  growing  narcissus  bulbs.  In  these  tests 
rotten  bulbs  containing  mites  were  placed  in  pots  of  soil  just 
below  the  healthy  ones  and  the  mites  readily  left  the  rotten  and 


122         CONNECTICUT   EXPERIMENT   STATION   BULLETIN   225. 

entered  the  healthy  bulbs.    Plate  I,  b,  shows  one  of  the  infested 
bulbs. 

Welsford'  claims  that  the  rot  of  narcissus  bulbs  is  transmitted 
by  the  minute  worm  or  nematode,  Tylenchus  devastatrix*,  and 
not  at  all  by  the  mite,  Rhizoglyphus  echinopus.  This  worm,  how- 
ever, has  not  been  found  in  many  of  the  rotten  bulbs  examined, 
while  in  few  cases  have  mites  been  absent  from  diseased  examples. 
Welsford  himself  admits  that  the  bulb  mite  does  a  great  deal  of 
damage,  but  he  does  not  consider  it  equal  in  importance  to  the 
nematode  as  a  carrier  of  disease. 

Life  History. 

Few  people  in  America  seem  to  have  studied  the  life  history  of 
the  bulb  mite.  The  most  recent  work  is  that  of  Yagi^,  a  Japanese, 
who  published  a  preliminary  note  on  the  life  cycle  in  1919.  In 
this,  he  makes  known  the  following  facts:  "The  mite  moults  twice 
and  the  duration  of  one  generation  is  about  ten  days  in  August, 
and  twenty  in  June.  Temperature  is  the  chief  factor  in  this  varia- 
tion and  has  an  important  effect  on  the  embryonic  development — 
the  number  of  eggs  laid  by  one  female  varied  from  9-59,  each 
being  dropped  singly  on  the  surface  of  the  bulb.  The  larva  is 
sluggish  and  bores  in  the  tissues  of  bulbs  and  grape  vines.  The 
adults  mate  within  2-8  hours  after  reaching  maturity  and  ovipo- 
sition  begins  on  the  day  of  mating.  The  life  of  the  female  is 
about  two  to  four  weeks  in  summer  while  that  of  the  male  is 
shorter." 

MichaeP  reports  one  case  in  which  he  reared  echinopus  from  egg 
to  adult  in  33  days.  He  observes  three  moults  instead  of  two  as 
noted  by  Yagi.  Careful  stucUes  by  the  writer  indicate  that  hya- 
cinthi  moults  three  instead  of  two  times,  thus  confirming  Michael's 
statement  in  this  regard.  When  hypopi  appear,  however,  four 
moults  accur  instead  of  three.  The  life  period  obtained  at  room 
temperature  60-75°  F.  (averaging  about  68°)  varied  from  17  to 
27  days;  with  temperature  ranging  from  70-80°  F.,  9-13  days.  The 
mite  becomes  torpid  at  50-55°  F.  and  at  about  95°.  The  air  in 
which  the  mites  lived  during  the  time  they  were  observed  was 
kept  as  near  optimum  humidity  as  possible,  which  condition  was 
judged  largely  by  daily  observance  of  the  amount  of  moisture 
contained  in  the  lens  paper  with  which  each  cell  was  provided. 

The  period  of  incubation  lasts  from  4-7  days.  A  six-legged 
larva  emerges  from  the  egg  and  the  mite  lives  in  this  condition 
3  to  8  days.     The  last  day  or  so  of  this  period,  sometimes  two 


*  Now  T.  dipsaci  Kiihn. 

^  Welsford,  E.  J.  Investigation  of  bulb  rot  of  narcissus.     Ann.  Appl. 
Biol.  82:  36-46:  1917. 

2  Yagi,  N.  Berichte  Ohara  Inst.  Landwirtsch.  Forschungen  I:   349-360: 
1918  Abstract  in  Rev.  Appl.  Ent.,  VII:  439-440:  1919. 

3  Michael,  A.  D.     British  Tyroglyphidae.     Vol.  II:  92-93:  1903. 


PLATE  I. 


a.     Flies,    (Scatopse  pulicaria  Loew)  with  hypopi  of  the 
bulb  mite  clinging  to  them,  enlarged  7  times. 


b.     Mite  infestation  just  beginning  in  a  growing  bulb.    Its  progress  is 
indicated  by  the  dark  lines  between  the  scales,  natural  size. 


PLATE  II. 


a.     Rotten   bulb  with  base  removed  showing   mites,   twice 
natural  size. 


b.     Bulb  completely  destroyed  and  containing  a  great  many 
mites,  natural  size. 


PLATE  III. 


a.     Mites  from  a  rotten  bulb,  enlarged  S  times. 


b.     Infestation   just   beginning  in  a  healthy   bulb,   natural 

size. 


A   STUDY    OF   THE    BULB   MITE.  123 

days,  is  spent  in  a  torpid  or  quiescent  condition  and  at  this  time 
the  larva  swells  so  that  the  separating  line  between  the  thorax 
and  abdomen  is  lost.  On  moulting  the  larva  acquires  two  addi- 
tional legs,  making  eight  in  all.  The  next  period,  which  may  be 
known  as  the  protonymph*  lasts  two  to  four  days,  after  which 
follows  a  second  quiescent  period  of  about  two  days  and  a  second 
moult  takes  place.  This  time  there  is  no  increase  in  the  number 
of  legs  or  much  change  in  form  unless  a  hypopus  or  resting  stage 
is  produced.  If  normal  in  form  the  mite,  now  known  as  the 
tritonymph*,  again  goes  into  the  quiescent  state  which  lasts  1-2 
days;  and  moults.  The  adult  mite  then  emerges.  If,  however, 
the  hypopial  state  appears  after  the  second  moult,  the  mite  may 
rest  for  one  or  two  weeks  or  more,  afterwards  moulting  and  giving 
rise  to  the  tritonymph.  The  latter  then  moults  and  the  adult 
mite  emerges  as  before. 

Adults  mate  a  day  or  so  after  becoming  mature  and  the  eggs  are 
soon  laid,  beginning  with  a  few  daily  at  first  and  later  increasing 
in  number  up  to  six  or  eight.  Two  females  observed  laid  ten 
eggs  per  day  for  four  successive  days,  but  this  is  rather  unusual. 
The  number  of  eggs  laid  has  been  found  to  vary  considerably, 
some  females  laying  more  than  one  hundred,  others  laying  only 
a  few.  One  individual  laid  130  eggs  in  all,  while  one  other  laid 
81,  and  still  another  59.  The  males  usually  die  shortly  after 
mating,  but  if  kept  separate  have  been  observed  at  this  laboratory 
to  live  for  more  than  two  months.  Females  also  live  from  one  to 
two  months  or  more  if  properly  fed  and  cared  for. 

The  following  shows  the  course  of  the  hfe  history: 

Cycle  in  which  hypopial  stage  is  skipped. 
Egg — larva — first  nymph — third  nymph — adult  female. 
Egg — -larva — first  nymph — third  nymph — dimorphic  male  adult, 

normal  male  adult. 

Cycle  with  hypopial  stage. 
Egg — larva — first  nymph — hypopus — -third  nymph — adult  female. 
Egg — larva — first  nymph^ — ^hypopus — third  nymph — ^dimorphic  male  adult, 

normal  male  adult. 

The  Dimorphic  or  Heteromorphic  Male. 

The  dimorphic  male  with  enlarged  third  pair  of  legs  (Fig.  2.  No.  10) 
has  been  thought  by  some  to  be  a  distinct  species,  but  it  has  been 
definitely  proven  by  others  to  be  merely  a  form  of  more  or  less 
infrequent  occurrence.  In  one  lot  of  mites  examined  36  males 
were  seen  without  encountering  a  single  dimorphic  forixi.  In  other 
lots  the  males  with  and  without  enlarged  legs  appeared  in  about 
equal  numbers.  The  dimorphic  males  breed  freely  and  the  off- 
spring consists  of  both  females  and  normal  and  heteromorphic 


*  The  hypopus  is  regarded  as  the  deutonymph,  and  is  frequently  inter- 
polated between  protonymph  and  tritonymph. 


124         CONNECTICUT   EXPERIMENT   STATION   BULLETIN   225. 

males.  One  specimen  was  seen  with  an  enlarged  third  leg  on 
one  side  and  a  leg  of  normal  size  on  the  other.  The  exact  function 
of  the  dimorphic  male  is  not  clearly  understood,  nor  do  we  under- 
stand the  causes  which  bring  about  such  remarkable  differences 
in  this  sex. 

The  Hypopus. 

Rather  complete  studies  of  the  hypopus  of  echinopus  have  been 
made  by  Michael  and  other  European  authorities,  and  it  is  now 
regarded  as  a  normal  period  in  the  life  history  of  the  mite.  Briefly 
explained,  it  is  a  form  similar  to  some  of  its  ancestors  which  is 
produced  from  time  to  time  from  no  apparent  reason  other  than 
a  strong  tendency  to  revert  to  type  and  "is  a  provision  of  nature 
for  the  distribution  of  the  species  occurring  irrespective  of  adverse 
conditions^".  Notwithstanding,  the  fact  remains  that  is  often 
impossible  to  distinguish  between  favorable  and  unfavorable  con- 
ditions and  it  seems  certain  that  conditions  promoting  their  develop- 
ment are  not  always  at  hand.  The  following  notes  relate  to  the 
development  of  the  hypopus. 

First  of  all  it  has  appeared  that  hypopi  are  much  more  numerous 
in  jars  where  the  bulbs  are  rotted  enough  to  leave  them  in  a  wet, 
sticky  condition.  Hypopi  are  produced  in  dry  as  well  as  moist 
cells,  but  more  rapidly  and  frequently  more  abundantly  in  the 
moist  cells.  This  was  demonstrated  by  use  of  a  moisture  gradient 
consisting  of  four  hanging  drop  slides  with  small  cells,  clamped  to 
a  larger  piece  of  glass  and  with  a  sheet  of  lens  paper  between ; 
one  end  of  the  gradient  being  placed  in  moist  sand,  and  each  cell 
provided  with  a  single  pair  of  mites  and  the  necessary  food.  The 
following  shows  the  results  of  three  tests  with  the  gradient 
described.  Cell  No.  1  in  each  case  was  in  contact  with  moist 
sand,  2,  3  and  4  further  away  in  the  order  mentioned.  These 
tests  were  then  repeated  with  similar  results. 


No.  of 

No.  of 

Per  cent. 

Date 

cell. 

mites. 

of  hypopi. 

Food  used. 

Begun.              Examined. 

1 

Ill 

27 

Unfermented 
dry  narcissus. 

May  14         July    7 

3 

83 

7 

a 

((         u                          u         u 

4 

90 

0 

11 

Fermented 

u        a                       a        a 

2 

39 

82 

hyacinth. 

<i        a                       a        a 

3 

14 

50 

(1 

It        u                       a        a 

4 

105 

0 

(I 
Fresh 

U          U                               (1          u 

1 

213 

25 

narcissus. 

July   24         Sept.  9 

2 

60 

10 

u 

u        a                       u        u 

3 

21 

0 

u 

11        a                      (t        ti 

4 

60 

0 

u 

u        a                       ti        u 

1  Michael,  A.  D.  The   hypopus   question,  or  the  life-history  of  certain 
Acarina.     Jour.  Linn.  Soc,  ZooL,  XVII;  389;  1884. 


A    STUDY    OF    THE    BULB    MITE.  125 

On  April  first  a  small  tightly  corked  bottle  was  provided  with 
about  an  inch  of  moist  sand  and  a  number  of  slices  of  potato 
previously  infested  with  the  bulb  mite.  These  ixiites  did  not  mul- 
tiply rapidly  but  reproduced  fairly  well  and  on  June  8,  100  indi- 
viduals were  counted  without  encountering  a  single  hypopus. 
Little  or  no  fermentation  took  place  in  the  bottle  until  after  this 
date  and  most  of  the  eggs  were  laid  on  the  outside  of  the  potato  and 
were  fairly  dry.  However,  where  the  potatoes  were  in  contact  with 
the  sand  there  was  considerable  moisture  surrounding  the  develop- 
ing mites.  Only  one  hypopus  was  seen  in  the  bottle  until  July  1. 
During  the  latter  part  of  July  mold  obtained  a  foothold  on  the  po- 
tato but  the  mites  continued  to  breed,  many  of  them  being  covered 
with  a  wet  sticky  film.  However,  even  under  such  conditions  less 
than  one  per  cent,  of  hypopi  developed — as  was  seen  by  examination 
on  September  9.  In  order  to  test  the  natural  ability  of  the  strain 
on  potato  to  produce  hypopi,  mites  were  transferred  to  glass  cells 
with  narcissus  or  hyacinth  at  several  different  periods  during 
the  course  of  the  experiment.  Hypopi  were  produced  abundantly 
in  practically  every  case  the  percentage  var^dng  from  10  to  80%. 
In  this  bottle  and  five  other  similar  ones  made  from  it  hypopi 
did  not  begin  to  appear  in  numbers  until  about  October  25,  making 
a  period  of  some  six  months  when  they  did  not  develop.  It  is 
difficult  to  explain  the  appearance  of  the  hypopus  in  small  cell 
transfers,  but  it  seems  as  if  some  necessary  change  in  conditions 
must  have  taken  place. 

Hypopi  developed  in  light  and  dark,  when  fed  on  decayed  and 
sound  food,  in  moist  and  dry  cells  and  apparently  when  warm 
and  cold.  They  also  developed  about  equally  well  when  the  food 
was  covered  with  small  amounts  of  sugar,  alcohol  (2%)  and  acetic. 
acid(l%). 

Michael  used  many  experiments  to  tr}'-  to  induce  certain  species 
of  Tyroglyphids  to  develop  without  producing  hj'popi,  but  failed; 
and  he  concluded  that  hypopus  is  a  noiTual  stage  in  their  develop- 
ment. Notwithstanding,  in  the  case  of  mites  like  the  bulb  mite 
in  which  all  individuals  do  not  pass  through  the  hypopus  stage, 
it  seems  hazardous  to  ascribe  such  a  phenomenon  entirely  to  the 
inherent  atavistic  tendency  or  natural  habit  of  the  individuals. 
It  is  well  known  that  in  a  somewhat  similar  life  cycle  found  in 
aphids,  reversion  to  the  sexual  forms  which  are  more  commonly 
skipped  are  induced  largely  by  changes  of  weather  and  food. 
Some  species  of  aphids,  moreover,  may  be  reared  continuously 
without  reversion,  when  proper  conditions  of  moisture,  temper- 
ture,  etc.,  are  maintained,  and  it  seems  as  if  something  similar 
must  be  true  of  the  mites  under  investigation,  caused  by  factors 
which  we  have  not  yet  learned  to  recognize. 

The  length  of  the  hypopus  stage  under  favorable  conditions 
is  usually  about  one  to  two  weeks. 


126       connecticut  experiment  station  bulletin  225. 

Migration  of  the  Species. 

The  hypopus  is  much  more  active  than  the  remaining  stages 
in  the  life  cycle  of  the  mite,  and  has  a  tendency  to  wander  from 
place  to  place.  It  will  also  attach  itself  to  any  moving  object.  At 
the  time  when  hypopi  become  numerous,  the  bulbs  are  commonly 
well  rotted  and  infested  by  numerous  small  fly  larvae,  one  of 
which  (Scatopse  pulicaria  Loew)  (Plate  I,  a)  was  found  in  large 
numbers.  The  flies  of  this  species  were  frequently  found  to  be 
literally  covered  with  hypopi  attached  by  means  of  their  ventral 
suckers.  Other  hypopi  were  seen  riding  peacefully  on  the  backs 
of  predaceous  mites,  and  still  others  have  been  found  attached 
to  lepidopterous  larvae.  The  mite  is  thus  afforded  an  admirable 
means  of  transportation,  of  wliich  it  is  capable  of  taking  full 
advantage  because  of  its  structure  and  habits. 

The  tables  below  show  the  length  of  the  various  stages  as  deter- 
mined at  this  laboratory. 


Tabular  Life  History  of  the  Bulb  Mite 


LENGTH  OF  EGG  STAGE. 

1919. 


Length  of  Number  Dates 

stage  days.  observed. 


Temperature  60°-75°  F. 
7  8  Sept.  29-Oct.  6. 

6M  3  Oct.  10-Oct.  17. 

7  4  Oct.  10-Oct.  17. 
63^                          4  Oct.  10-Oct.  17. 

1920. 
Temperature  70°-80°  F. 
4  2  July  15-July  19. 

3  2  July  16-July  19. 

4  3  July  16-July  20. 
4                              8  July  16-July  20. 

LENGTH  OF  LARVAL  STAGE. 

Length  of  Number  Dates, 

stage  days.  observed. 

1919. 
Temperature  60°-75°  F. 

8  1  Oct.    3-Oct.  10. 

6  1  Oct.    6-Oct.  11. 

7  2  Oct.  6-Oct.  12. 
6  2  Oct.  17-Oct.  21. 
6  1  Oct.  17-Oct.  22. 
6  2  Oct.  17-Oct.  22. 
63^  2  Oct.  16-Oct.  21. 

1920. 
Temperature  70°-80°  F. 

2  2  July  19- July  21. 

3  8  July  20- July  23. 

3  2  July  18-Julv  21. 

4  1  July  lO-July  23. 

5  3  July  19-July  24. 


A    STUDY    OF   THE    BULB    MITE. 


127 


LENGTH  OF  FIRST  NYMPHAL  STAGE  (PROTONYMPH). 


Length  of 
stage  days. 


Number 
observed. 


Temperature  60°-75°  F. 


Dates. 
1919. 


1 
1 
1 
1 
1 
1 
1 
1 
1 

Temperature  70^ 
1 
1 
1 
2 
2 


13. 
15. 
15. 
11. 
12. 
24. 
24. 


-80' 


Nov.  10-Nov 
Nov.  12-Nov 
Nov.  11-Nov 
Nov.  8-Nov 
Nov.  8-Nov 
Nov.  16-Nov 
Nov.  19-Nov 
Nov.  20-Nov.  23 
Nov.  20-Nov.  22 

1920. 
F. 

July  21- July  23. 
July  21-July  23. 
July  21-July  23. 
July  21-July  22. 
July  21-July  23. 


LENGTH  OF  HYPOPUS  STAGE  (DEUTONYMPH). 


Length  of 
stage  days. 


12 
7 
5 
7 

13 


Number 
observed. 


Tempera 


Dates. 

1920. 


ure  65°-75°  F. 


March  15-March  27. 
March  29-April  5. 
April  17-April  22. 
April  10-April  17. 
April  10-April  23. 


LENGTH  OF  THIRD  NYIVIPHAL  STAGE    (TRITONYMPH). 

Length  of  Number  Dates, 

stage  days.  observed. 

1919. 
Temperature  60°-75°  F. 
4  1  Nov.  15-Nov.  19. 

3  1  Nov.  11-Nov.  14. 

4  1  Nov.  12-Nov.  16. 
3                              1  Nov.  24-Nov.  27. 

3  1  Nov.  23-Nov.  26. 

4  1  Nov.  22-Nov.  26. 

1920. 
Temperature  70°-S0°  F. 
3  1  July  23-July  26. 

3  1  Julv  24-July  27. 

2  1  July  25-July  27. 

3  1  July  24-July  27. 
2  1  July  23-July  25. 
2  2  July  22-July  24. 
2      .                        1  July  23-July  25. 

Variations  obtained  in  length  of  life  cj'cle  9-29  days    (with  hypopus 
absent  from  the  cycle);  with  hypopus  included  14-42  days. 

Other  Species  of  Mites  and  Predaceous  Enemies. 

Several  predaceous  mites  (Parasitidae)  and  the  Tjrroglyphid, 
Histiostoma  rostro-serratus  have  been  found  frequently,  but  the 


128  CONNECTICUT   EXPEEIMENT   STATION   BULLETIN   225. 


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130         CONNECTICUT   EXPERIMENT   STATION   BULLETIN   225. 

latter  seems  to  flourish  best  in  wet  rotten  bulbs  and  has  not  been 
observed  to  feed  on  healthy  tissue.  The  small  hypopus  of  this 
species  is  produced  abundantly  and  frequently  attaches  itself  to 
Rhizoglyphus  or  any  insect  which  lives  within  the  bulbs.  Histi- 
ostoma  is  much  smaller  than  Rhizoglyphus  as  is  also  the  hypopus, 
compared  with  that  of  the  bulb  mite.  When  observed  feeding 
the  adult  is  much  lighter  in  color  and  the  caudal  margins  of  the 
abdomen  are  less  rounded.  The  predaceous  species  (Laelaptini) 
are  very  active  brown  mites  slightly  larger  than  the  true  bulb 
mite.  In  one  box  of  bulbs  containing  about  one-fourth  bushel, 
these  enemies  became  very  numerous  and  were  seen  running  about 
over  the  bulbs  like  ants.  Doubtless  they  had  destroyed  many 
bulb  mites.  In  another  case  a  Mason  jar  containing  many  bulb 
mites  was  entirely  cleared  of  Rhizoglyphus  in  about  a  month  after 
the  predaceous  species  was  first  noticed  in  the  jar. 

The  small  Cecidomyid  fly  Lesiodiplosis  sp.  *  was  also  found 
feeding  upon  the  bulb  mite.  The  larva  is  a  small,  pinkish  maggot 
about  one  mm.  in  length,  which  crawls  about  among  the  mites 
and  feeds  on  them. 

Control  Measures. 

Morphological  studies  show  that  the  mite  has  no  tracheal  system 
and  cannot  be  killed,  theoretically,  by  ordinary  fumigants.  Ewing^ 
demonstrated  that  4.1  oz.  of  potassium  cyanide  per  5470  cu.  ft. 
or  1  oz.  per  133  cu.  ft.  of  air  space  was  insufficient  to  kill  the  bulb 
mite.  Fumigation  at  tliis  laboratory  with  carbon  disulphide  in 
an  air  tight  container,  1  oz.  to  100  cu.  ft.  required  48  hours  to 
obtain  a  good  Idll.  Mites  on  the  interior  of  the  bulbs  were  not 
killed  even  with  this  length  of  exposure.  Sorauer^  recommends 
for  use  against  the  mite,  R.  echinopus,  the  use  of  a  48  hour  carbon 
disulphide  fumigation  or  immersion  in  tobacco  extract.  40% 
nicotine  sulphate  1-400  with  the  addition  of  soap  Idlled  only  7.1% 
in  tests  conducted  here.  Fir  tree  oil  was  considerably  more  effi- 
cient, killing  60-90%  in  some  instances,  wliile  in  bulbs  soaked  in 
water  heated  to  55°  C.  nearly  100%  were  killed.  Woods^  treated 
bulbs  with  mercuric  chloride  1-1000  and  1-2000,  formalin  1-1000  and 
1-2000  without  success.  A  good  kill,  however,  was  obtained  by 
the  writer  with  formalin  heated  to  50°  C.  (122°  F.),  the  bulbs 
being  left  for  a  period  of  ten  minutes.  Nicotine  sulphate  1-400 
heated  to  50°  C.  (122°  F.)  and  nicotine  oleate  heated  to  50°  were 
also  very  successful  acaricides. 

In  all  cases  careful  observations  were  made  on  the  hypopus 
because  of  its  greater  resistance,  and  the  mites  were  examined 
daily  for  three  days  after  treatment  to  be  sure  of  results. 

*  Determined  by  Dr.  E.  P.  Felt. 

lEwing,  H.  E.     Oregon  Agr.  Exp.  Sta.  Bui.  121:  70:  1914. 
^SorauerP.      Pflanzenkrankheiten  III:  109:  1913. 
5  Woods,    A.    F.     U.  S.  Dep.  Agr.,  Div.  Veg.  Phy.  &   Path.,  Bui.  14: 
1897. 


A   STUDY   OF   THE    BULB   MITE. 


131 


For  convenience,  the  different  treatments  and  practices  for  control  of 
the  pest,  will  be  enumerated. 

Unsuccessful  Treatments. 

1.  Hydrocyanic  acid  gas  (HCN)  fumigation,  the  gas  obtained  by  using 

potassium  cyanide  1  oz.  to  133  cu.  feet  of  air  space^. 

2.  Carbon  disulphide  1  oz.-lOO  cu.  feet — '24  hr.  fumigation. 

3.  Formalin  1  part-lOOO  parts  water  and  1  part-2000  parts  water — cold^. 

4.  Nicotine  sulphate  1  part-400  parts  water  plus  soap  2  lbs.-50  gals. — cold. 

5.  Schnarr's  insecticide  1  part-100  parts  water. 

6.  Scalecide  1  part-15  parts  water. 

7.  Mecuric  chloride  1  part-lOOO  parts  water  and  1  part-2000  parts  water"^. 

Partly  or  Entirely  Successful  Treatments. 

1.  Carbon  disulphide  1  oz.-lOO  cu.  feet — 48  hour  fumigation. 

2.  Nicotine  sulphate  1-400  heated  to  50°  C.  (122°  F.)— bulbs  immersed 

for  10  min.     Also  nicotine  oleate  at  the  same  temperature. 

3.  Formalin  (2%)  heated  to  50°  C;  bulbs  immersed  for  10  minutes. 

4.  Hot  water  55°  C.  (131°  F.) — bulbs  immersed  for  10  minutes. 

Practices  of  Value  in  Getting  Rid  of  the  Mite. 

1.  Selection  of  bulbs  to  be  planted;  all  soft  and  rotten  bulbs  to  be  dis- 

carded. 

2.  Proper  care  and  fertilization  of  the  growing  plants. 

3.  Cold  storage  33-35°  F.  (any  temperature  below  50°  F.)  to  prevent 

multiplication  of  the  mites  while  stored. 

Tests  of  Treatments  for  Narcissus  Bulbs  to  Determine 
WHAT  Injury  if  any  Results  Therefrom. 


Insecticide 
Used 

Temperature 

of 

Insecticide 

Period  of 

Treatment 

Date  of 

Treatment 

Amount 

of 
Injury 

Date  of 
Examination 

No.  of  bulbs 

per 

Treatment 

Nicotine  Sulphate 

1-400 

Soap  (2  lbs.— 50  gals.) 

50°  C. 

10  min. 

1920 
Aug.  31 

None 

1920 

Nov.  28 

10 

Nicotine  Sulphate 

1-400 

Soap  (2  lbs.— 50  gals.) 

50°  C. 

5  min. 

Aug.  31 

None 

Nov.  28 

10 

FormaUn  2% 

50°  C. 

10  min. 

Aug.  31 

None 

Nov.  28 

10 

Nicotine  Sulphate 
1-400 

50°  C. 

10  min. 

Aug.  31 

None 

Nov.  28 

10 

Nicotine  Sulphate 

1-400 

Soap  (2  lbs.— 50  gals.) 

45°  C. 

10  min. 

Aug.  31 

None 

Nov.  28 

9 

Nicotine  Sulphate 

1-400 

Soap  (2  lbs.— 50  gals.) 

45°  C. 

5  min. 

Aug.  31 

None 

Nov.  28 

10 

Check,  no  treatment 

Aug.  31 

None 

Nov.  28 

10 

lEwing,  H.  E.    Oregon  Agr.  Exp.  Sta.,  Bui.  121:   70:    1914. 

2  Woods,  A.  F.    U.  S.  Dep.  Agr.,  Div.  Veg.  Phys.  and  Path.,  Bui.  14:    1897. 


132         CONNECTICUT   EXPERIMENT   STATION   BULLETIN   225. 

A  few  tests  were  conducted  with  narcissus  bulbs  in  order  to 
be  sure  that  no  injury  results  from  the  more  successful  treat- 
ments. Ten  narcissus  bulbs  were  first  heated  to  59-65°  C.  in 
hot  water  and  left  for  a  period  of  one-half  hour.  Two  bulbs  were 
retained  as  checks.  All  treated  bulbs  were  killed,  but  tlie  checks 
remained  healthy  and  grew.  Shortly  after,  two  narcissus  '>ulbs 
were  treated  with  hot  water  at  a  temperature  of  50*^  T'  ;  ten 
minutes.  These  bulbs  had  fresh  roots  about  one  h^-n  m  length. 
Two  bulbs  were  retained  as  checks.  All  bulbs  ii,rew,  but  the 
untreated  were  seen  to  be  in  better  condition  at  rime  of  blooming 
and  on  removing  from  the  pots,  the  original  roots  of  the  treated 
were  found  to  be  dead  and  a  new  lot  in  their  place.  The  table 
above  is  a  continuation  of  these  tests  and  shows  that  a  temperature 
of  50°  C.  is  non-injurious  to  narcissus,  if  the  bulbs  are  without  fresh 
roots  and  the  period  of  immersion  is  not  great. 

Paper  white  narcissus  were  used  in  these  tests  and  none  of  the 
bulbs  had  any  fresh  roots.  Some  of  the  treated  bulbs  grew  better 
and  were  more  vigorous  than  the  checks.  All  bulbs  grew  and  the 
plants  were  approximately  the  same  height  at  the  conclusion  of 
the  test. 

Conclusions. 

1.  The  bulb  mite  is  capable  of  injuring  healthy  growing  bulbs. 

2.  It  is  spread  from  place  to  place  chiefly  by  means  of  the 
hypopus,  which  clings  to  small  flies  emerging  from  the  decayed 
bulbs. 

3.  The  life  cycle  may  be  completed  in  less  than  a  month  (9-29 
days),  or  may  be  extended  to  a  month  and  a  half  if  the  hypopial 
stage  develops  or  if  adverse  conditions  prevail. 

4.  One  of  the  most  satisfactory  means  of  Idlling  the  mites 
was  found  to  be  that  of  dipping  the  bulbs  in  nicotine  sulphate 
1-400  or  nicotine  oleate,  heated  to  50°  C.  Hot  water  (50°  C.) 
also  kills  a  good  percentage. 

5.  The  authority  commonly  given  for  the  scientific  name 
should  be  changed  to  Banks  and  the  name  should  read  Rhizo- 
glyphus  hyacintki  Banks. 


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